CR-1-554
SURVEY OF THE STATE OF KNOWLEDGE OF SOURCES OF
NATURALLY EMITTED REACTIVE HYDROCARDONS
INTO THE ATMOSPHERE
FINAL REPORT
Contract No. 68-03-2034
Program Element 1AA006
by
A. Q. Eschenroeder
September 1974
Project Officer
Dr. Lawrence Raniere
National Ecological Research Laboratory
National Environmental Research Center
Corvallis, Oregon 97330
GENERAL
RESEARCH WO CORPORATION
P.O. BOX 3587, SANTA BARBARA, CALIFORNIA 93105
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
-------
In addition to approval by the Project Leader
and Department Head, General Research Corporation
reports are subject to independent review by
a staff member not connected with the project.
This report was reviewed by S. F. Kornish.
The work upon which this publication is based was
performed pursuant to Contract No. 68-03-2034 with
the Environmental Protection Agency.
-------
CR-1-554
SURVEY OF THE STATE OF KNOWLEDGE OF SOURCES OF
NATURALLY EMITTED REACTIVE HYDROCARBONS
INTO THE ATMOSPHERE
Contract No. 68-03-2034
Program Element 1AA006
by
A. Q. Eschenroeder
September 1974
Project Officer
Dr. Lawrence Raniere
National Ecological Research Laboratory
National Environmental Research Center
Corvallis, Oregon 97330
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
-------
ABSTRACT
In this report the present scientific state of knowledge is reviewed
for sources of naturally emitted reactive hydrocarbons. The literature
is surveyed first to determine current thinking on the origins and natural
emission rates of these reactive hydrocarbons compared with anthropogenic
emission rates of the same classes of hydrocarbons. Measurements of
atmospheric concentrations in remote areas are cited and atmospheric
reaction mechanisms are explored in an effort to characterize the trans-
formation and fate of these hydrocarbon species. In conclusion, both the
state of knowledge of emission rates and that of atmospheric levels and
processes are evaluated. Finally, preliminary recommendations for future
work are made for further measurements covering oxygenated hydrocarbon
compounds and analysis of the reactive diffusion of compounds from plant-
covered areas of the earth's surface. The recommended analysis can be
done using available data to test the internal consistency of various
measurements that have been reported in the literature. This could be
done using existing techniques.
This report was submitted in fulfillment of Contract No. 68-03-2034
by General Research Corporation under the sponsorship of the US
Environmental Protection Agency.
-------
ii
-------
CONTENTS
SECTION PAGE
ABSTRACT i
1 INTRODUCTION 1
2 ORIGINS AND NATURAL EMISSION RATES 2
3 ATMOSPHERIC CONCENTRATIONS AND TRANSFORMATIONS 11
4 CONCLUDING REMARKS AND PRELIMINARY RECOMMENDATIONS 18
4.1 Summary of Observations and Evaluation 18
4.2 Preliminary Recommendations 22
REFERENCES 25
iii
-------
iv
-------
TABLES
NO. PAG1
2.1
2.2
2.3
2.4
Estimated Release of Terpene-Type Hydrocarbons from
Vegetation
World-Wide Hydrocarbon Emission Estimate
Emissions of Major Eastern US Forest Trees
Emissions of Major Western US Forest Trees
4
5
8
8
2.5 Rate of Foliar Isoprene Accumulation in a Closed
Atmosphere 9
2.6 Estimation of Total Contribution to Atmosphere from Rate
of Foliar Terpene Accumulation in a Closed Atmosphere 9
2.7 World-Wide Terpene Emission Estimates 10
3.1 Carbon Monoxide and Organics in the Atmosphere, Pt. Barrow,
Alaska; 24-hr Analysis, September 2-3, 1967 14
3.2 Reactivity and Products of Photochemical Oxidation of 5
ppm Each HC + N02 16
4.1 Summary of Literature Reviewed in Order of Reference
Number 19
-------
vi
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1 INTRODUCTION
This survey is carried out in order to meet the need of the US En-
vironmental Protection Agency to characterize our present scientific know-
ledge about the natural emissions of reactive hydrocarbons. To understand
haze formation and background pollutant levels, it is of interest to know
the emission rates of hydrocarbons asi" they depend on the type of land sur-
face, the type of vegetation, and the type of atmospheric environmental
conditions. The survey is based on a review of the major literature deal-
ing with this subject. The scope of the review encompasses recent pub-
lished scientific work in the fields of natural emissions, atmospheric
transformation, and the ultimate fate of reactive hydrocarbons emanating
from diverse land surfaces outside of urban regions.
This report is organized in three main sections. The first covers
the origins and natural emission rates of reactive hydrocarbons, and is
based on actual measurements, on calculations, and in some cases on sheer
speculation. These rates are compared with those from man-made emissions
occurring mostly in urban areas. Wherever possible, identification of
compounds are made and measured values are cited with respect to the type
of vegetative cover on the nearby land surface. The second section deals
with the measurements of atmospheric concentrations that have been made
at various times. Along with these measurements have been offered vari-
ous hypotheses regarding reaction mechanisms of the naturally emitted reac-
tive hydrocarbon substances in the atmosphere. Such reaction mechanisms
may be involved with background ozone levels. A detailed understanding
of the origins of background ozone levels is essential in designing air
quality control strategies because the national ambient air quality standard
is only a few parts per hundred million above what most people believe to
be background levels. The final section of this report evaluates the
state of knowledge of both the emissLon rates and atmospheric processes
of naturally occurring reactive hydrocarbons. In this context, recommen-
dations are made in a preliminary fashion for future work to characterize
the naturally emitted hydrocarbons more completely, and test the Internal
consistency of the measurements by reactive diffusion analysis.
-------
2 ORIGINS AND NATURAL EMISSION RATES
The first contribution we shall review in the time period of interest
1 2
is that of F.W. Went ' regarding the appearance of organic matter in the
atmosphere and its relationship with petroleum formation. These papers
also deal with the question of blue haze formation in the atmosphere due
to the presence of this naturally emitted organic matter. Went postulates,
by mass balances on decomposing and metabolizing plant materials, that iso-
prene derivatives volatilize as they oxidize. He suggests the examples of
an aer:.al alga called trentepholia, as well as the examples of land covered
by sagebrush and coniferous forests. The emission estimates are based on
0.1% of the plant material being carotenoids, and 0.05% phytyl of chloro-
phyll plus 5% of all photosynthates. These percentages, then, represent
the basis for the emissions estimate. For sagebrush, Went estimates 10
5 2
tons per year over a 2 x 10 km area. In the Western United States, using
the same estimate of flux density, he arrives at 5 x 10 tons per year over
7 2
a 10 km area of coniferous forest cover. Summing over the contributions
from these, as well as hardwood forests, cultivated lands, and steppes, he
o
arrives at a total of 10 tons per year of volatile hydrocarbon-like com-
pounds that are synthesized by plants, all based on the 5% of all photo-
synthates being released as hydrocarbons. Adding to this 7.5 x .10 tons
of material from the carotenoid decomposition, he obtains a total of
a
1.75 x 10 tons of volatile organic material emitted each year over the
entire surface of the earth.
Rasmussen and Went actually carried out measurements of concentra-
tions of terpenoids such as isoprene, a-pinene, $-pinene, A-carene, myrcene,
a-limonene, and paracymene. Measurements were carried out in the West
Plains area of the Ozark Mountains in Missouri. The measurements exhibited
decreases in emission rate during four successive days of rain in some of
the other tests carried out in the Smokey Mountain area. High emissions
were associated with waves of leaves dying in the autumn. They also found
out that an oak forest emits as much volatile material as a coniferous
forest except that lower odor-level species are present in that case.
-------
The species were identified as having the same absorption properties as
isoprene in a gas chromatograph. Actual emissions estimates were made
using various approaches. Using an average global concentration of 10 ppb
in the air, they calculate a worldwide emission rate of 43.8 x 10 tons
per year. The explanation of how the calculation was carried out using
2
a 1-cm air column extending up to 2 km in altitude is rather obscure.
Rasmussen and Went estimated a total global emission of 20-40 x 10 tons
per year carrying out calculations from concentration measurements that
were obtained by enclosing foliage in a plastic bag and taking air samples
from the bag. They concluded from crushing the foliage and then taking
measurements that the terpenes are always produced, but they are only
released when the leaves age and die. A third method that they employed
for making emissions estimates was based on measurements taken within a
plastic covered frame 1 m x 1 m in area having a height of 65 cm.
This frame was placed over a small plot of vegetation, and air exchange
was allowed by punching hundreds of small holes through the side of the
cover. This was later reported to give an emission estimate of 13.5 x 10
tons per year for worldwide terpene emissions; however, this value was not
corrected for the vertical foliage area over the ground area.
4
In a paper presented before the American Chemical Society, Ripperton,
et al., came up with global emission estimates that were two to ten times
the previous estimates. Their main objective was the study of the rela-
tion of reaction between a-pinene and ozone in the atmosphere. In an
effort to study atmospheric transformation processes, they asserted that
terpene compounds would consume 7.8% of the atmospheric ozone using a very
approximate method of estimating the reaction rate.
Robinson and Robbins surveyed the sources, abundance, and fate of
gaseous atmospheric pollutants for a wide variety of compounds including
reactive hydrocarbons. They considered both natural and anthropogenic
sources of these compounds. They summarized Went's figures in accordance
with the values shown here in Table 2.1. Shown are the contributions
-------
TABLE 2.1
ESTIMATED RELEASE OF TERPENE-TYPE HYDROCARBONS FROM VEGETATION5
m - . Estimated Emanations,
Type of Vegetation tons/year
Coniferous Forest 50 * 10
Hardwood Forest
,6
Cultivated Land
50 x 10
Steppes
Carotene Decomposition of Organic Material 70 x 10
170 x 106
from coniferous forests, hardwood forests, cultivated lands, steppes, and
Q
carotene decomposition, as outlined above, totaling 1.7 x 10 tons per
Q
year. This is to be compared with 0.27 x 10 tons per year of reactive
hydrocarbon emissions from anthropogenic sources. These sources are sum-
marized in Table 2.2 extracted from Robinson's and Robbins' report. It
should be noted in making this comparison between natural and man-related
emissions that the land areas over which these emissions occur differ
widely and consequently the local impacts of the emissions on photochemi-
cal air pollution vary widely.
Using gas chromatography, Rasmussen identified isoprene as one of
the frequent leaf emissions observed from plants that was measured in
numerous past studies. The chromatographic analyses were cross-checked
with infrared analysis and mass spectrometric analysis in order to narrow
down the identification to the cited compound. These findings seem con-
sistent with those reported in a study of hydrocarbon precursors of carcino-
genic substances in tobacco smoke. That study presented evidence sup-
porting the role of terpenic tobacco components in the formation of aro-
matic compounds. It was determined that the composition of tobacco smoke
shows isoprene, dipentene, and Cg-aromatics. It was stated "isoprene
-------
TABLE 2.2
WORLD-WIDE HYDROCARBON EMISSION ESTIMATE5
Source
Coal
Power
Industrial
Domestic and
Commercial
Petroleum
Refineries
Gasoline
Kerosene
Fuel Oil
Residual Oil
Evaporation and
Transfer Loss
Other
Solvent Use
Incinerators
Wood Fuel
Forest Fires
Source
Quantity,
tons
(x 106)
1,219
1,369
404
11,317
bbl
379
100
287
507
379
3
500
466
324
Emission
Factor,
Ib/ton
0.2
1.0
10
56 tons/
10,000 bbl
180
0.6
1.0
0.9
41
30 lb/yr/
person
100
3
7
Percent
Reactive
15%
15%
15%
14%
44%
18%
18%
18%
20%
15%
30%
15%
21%
Total
Emission,
tons
(x 106)
0.2
0.7
2.0
6.3
34
<0.1
0.1
0.2
7.8
10
25
0.7
1.2
88.3
Reactive
Emission,
tons
(x 104)
3
10.5
30
88
1,500
1
1.8
3.6
156
150
750
10.5
25
2,729.4
-------
constitutes 50%-80% of the total unsaturated gaseous hydrocarbons present
in tobacco smoke." In that study it was noted that the isoprene tars are
carcinogenic probably due to the component of 3,4-benzpyrene that is
found in these tars.
Returning to Rasmussen's identification of isoprene one should note
that the studies were carried out in leaf assimilation chambers of 2 liters
2
volume and involved 300-500 cm area samples of foliage. After these sam-
ples were irradiated for about 2 hours, 1-ml gas samples were withdrawn
and analyzed. The presence of isoprene was detected by gas chromatographic
analysis for more than 30% of the 230 plant species that were examined.
Moreover, in situ studies were made by analyzing the air over the foliage
canopy of mango leaves. These gave levels of 0.6 ppb isoprene. When the
sampler was loosely sheltered with a paper cone, the readings rose to 24
ppb isoprene indicating the mango leaves were emitting this hemiterpene
substance.
A search of Rasmussen's references indicates, however, that similar
Q
observations were made earlier in the USSR by Sanadze and Dolidze. They
irradiated amorpha fruti-oosa, buxus, and quercus iberiaa in intense light
for 1-2 hours at a temperature of 20-30°C. Samples of the air surround-
ing these plants were condensed and were analyzed mass spectrometrically.
Experimental samples displayed peaks at a molecular weight of C,.H_, which
is isoprene. Peaks were also displayed at the molecular weights of butane,
propane, and some lower alcohols. The authors warn in their abstract that
the butane detection might be an artifact. The samples were condensed in
liquid nitrogen and were separated by the gas chromatograph prior to de-
tection in the mass spectrograph. In order to run a control, room samples
in the experimental room were checked against air samples from the con-
trol room.
q
Hancock, Applegate, and Dodd found anthracene, fluoranthene, pyrene,
benz(a)pyrene, and benzo(a)pyrene on the leaves of little blue stem and
-------
post oak. They analyzed the dry plant material and found it to contain
5-110 micrograms per kilogram of these materials. However, they mentioned
nothing about the plants emitting them. Presumably the emissions would
be lower than those of terpene because of the lower vapor pressure of
these materials. They ran a control near a railroad right-of-way in an
effort to test whether the polynuclear aromatic hydrocarbons were deposited
on the leaves from man-made sources. It is known, for example, that diesel
exhaust contains these classes of hydrocarbons. Based on this control,
they concluded that most of the polynuclear aromatics were derived from
plant synthesis and not from deposition due to diesel exhaust.
An update of the work on emissions of hydrocarbons from trees was
made by Rasmussen in an article wherein he surveyed types of trees with
relationship to the emitted chemical compounds, the rates of emissions
from selected types of plants, and the foliar emission rates that might
be ascribed to plant sources of isoprene and a-pinene. In this survey is
found a detailed discussion of the geographical distribution of tree types
within the United States. This discussion carried forward to assess the
dependence of terpenoid emissions on leaf type, age, and temperature. It
is stated that the emissions of hemiterpene additionally depends on light
intensity. Tables 2.3, 2.4, and 2.5 summarize the findings in Ref. 10.
In order to obtain emissions, Rasmussen converts ppb/hr to metric tons
per unit canopy depth. He assumes that the emissions are homogeneously
mixed within 1 liter of air and that the molecular weight of the emis-
sions equals that of air. He further finds that it is necessary t:o assume
a vegetation canopy depth. These estimates are summarized on Table 2.6.
Rasmussen further notes how widely the estimates of emissions vary depend-
ing upon the method employed to derive them. The range of values is
indicated by a comparison of the findings enumerated in Table 2.7. It
should be noted that the estimate of anthropogenic sources of reactive
hydrocarbons world-wide is 27 x 10 tons per year which lies near the
lower end of the range of natural reactive hydrocarbon emission estimates
shown in Table 2.7.
-------
TABLE 2.3
EMISSIONS OF MAJOR EASTERN US FOREST TREES
10
Softw
Emit o-Pinene
White Pine
Red Pine
Jack Pine
Longleaf Pine
Slash Pine
Shortleaf Pine
Loblolly Pine
Hemlock
White Cedar
Larch
Spruce
Fir
Balsam Fir
Cypress
Dods
Emit Isoprene
Oak
Sweetgum
Sycamore
Willow
Cottonwood
Balsam Poplar
Aspen
Hardw
Emit Isoprene and
a-Pinene
Sweetgum
Yellow Poplar
Balsam Poplar
Spruce (Softwood)
aods
Type of Emission
Unidentified
Hickory
Blackgum
Beech
Birch
Maple
Ash
Black Walnut
Hackberry
Basswood
TABLE 2.4
EMISSIONS OF MAJOR WESTERN US FOREST TREES
10
Softwoods
Hardwoods
Emit a-Pinene
Foiiclerosa Pine
Jeffrey Pine
Sugar Pine
Limber Pine
Western White Pine
Lodge Pole Pine
Grand Fir
White Fir
Alpine Fir
Western Hemlock
Western Red Cedar
Douglas-Fir
Redwood
Larch
Sitka Spruce also Isoprene
Engolmann Spruce also Isoprene
Colorado Blue Spruce also I sop rent;
limit Isoprene
Aspen
Buckthorn
Type of Emission
Unidentified
Tanoak
Red Alder
-------
TABLE 2.5
RATE OF FOLIAR ISOPRENE ACCUMULATION IN A CLOSED ATMOSPHERE
10
Plant
Oak
Sweet-Gum
Eucalyptus
Cottonwood
Units
2
ppb/min/in
2
ppb/min/in
2
ppb/min/in
2
ppb/min/in
Light Intensity
(foot candles)
50
0.04
0.02
340
0.40
0.21
0.26
0.31
700
1.7
0.70
0.83
1.2
1200
2.4
1.4
NOTES: Conditions: bell jar, 1 liter; temperature, 28°C.
Values are means of six replicated measurements on same plants.
TABLE 2.6
ESTIMATION OF TOTAL CONTRIBUTION TO ATMOSPHERE FROM RATE
OF FOLIAR TERPENE ACCUMULATION IN A CLOSED ATMOSPHERE
Region
Vegetated
Earth Surface
Total US
Area
Commercial
US Forests
Area , cm
io18
1017
2 x 1016
Metri
10
23.4
2.34
0.47
c Tons (1
Depth
50
117
11.7
2.4
O6) per
in cm
75
175
17.5
3.5
Canopy
200
464
46.4
9.4
NOTES:
Conditions: Rate: 100 ppb/hour; daily output 10 hr/day; annual
output 180 days/yr; volume enclosed, 1 liter; land area enclosed,
10 cm2.
Calculation: Rate (% vol.) x weight of 1 liter of air (converted
to weight in percent) x daily output (hr) x annual output (days)
2 2 9
x vegetated surface of region (cm )/area enclosed (cm ); 100 x 10
x 1.3 gm/1 x 10 hr x 180 days x io18 cm2/10 cm2; 23.4 x io6 metric
tons/yr for earth's vegetation at depth of 10 cm.
-------
TABLE 2.7
WORLD-WIDE TERPENE EMISSION ESTIMATES
10
Investigator
Method
Estimate in Tons
Went
Sum of sagebrush emission ter-
penes as percentage of plant
tissues
175 * 10
Rasmus.sen and
Went3
1. Bagging foliage 1 liter/
10 cm2
2. Structure enclosing 0.65
3, 2
m /m
3. Direct in situ ambient
concentration
23.4 x 10
13.5 * 10
432 x 106
6*
6*
Ripperton, White
4
and Jeffries
Reaction rate 0,/pinene
2 to 10 x previous
estimates
Not corrected for vertical foliage area over ground area.
10
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3 ATMOSPHERIC CONCENTRATIONS AND TRANSFORMATIONS
The impact of naturally emitted reactive hydrocarbons on the earth's
atmosphere involves what becomes of these compounds once they are emitted
.in addition to the details of their origins. Most of the research work
dealing with the sources has also addressed the problem of the transport
and fate of the organic matter in the atmosphere.
1 2
In his papers already cited, ' Went argues that atmospheric ozone
attacks the emitted reactive hydrocarbon compounds and that blue haze par-
ticles are ultimately formed. The blue color is derived from the property
that the particles are hypothesized to be less than 0.1 pm in diameter.
A long discussion is presented in an effort to rule out dust and other
possible origins of haze occurrence. Meteorological explanations are
offered involving the visibility of sun rays, the ozone peak in the tropo-
sphere, and the occurrence of red sunsets in support of the blue haze
hypothesis. Most of these arguments constitute circumstantial evidence,
however, as to the origins of the atmospheric aerosol. Went concludes
that the bituminous or asphaltic composition of the blue haze is reflected
in the composition of rainwater residues which are constituted of 40%-70%
organic material.
4
Ripperton, White and Jeffries deal primarily with the gas phase
reactions of ozone on pinenes. They hypothesize that the initial attack
reaction is bimolecular, but they have difficulty determining a rate con-
stant because of a multiplicity of chain branches arising from reactions
with decomposition products. Observations indicate a bimolecular rate
constant in excess of 10 liters'mole -s . The decrease of a-pinene
relative to the decrease in ozone at times exceeded a factor of 10.
Experiments ascertained that a-pinene concentrations remained stable in
the mylar bag samples. Compared with 8-pinene, a-pinene reacted more
slowly with ozone, and the consumption ratio of 6-pinene to 0~ wan also
greater than 1. These workers used Went's figure for terpenoid produc-
tion from natural sources and estimated that these compounds would be
11
-------
responsible for consuming some 8% of the atmospheric ozone. Accounting
for the stoichiometry of the pinene consumption, however, they believed
that the percentage would be closer to 5%-50% of the 8% figure. This
tends to indicate that the ozone pinene reactions represent a significant
sink for the terpenoids, but are probably of relatively minor importance
as a sink for atmospheric ozone. It should be noted that these authors
use Went's figure for terpenoid emissions when, according to Rasmussen,
in the complete form of Ref. 10 they derived their own emission rate
which was 2-10 times higher than any of the other estimates.
An end product of the ozone reaction sequence with the terpenes may
be manifested as Aitken condensation nuclei according to the studies of
Went. Normally, the presence of Aitken condensation nuclei is an indi-
cation of combustion emissions of pollutants. The condensation nuclei
are hypothesized to form by polymerization of photooxidation products of
the ozone terpene reaction. Went extends his argument along classical
lines citing carefully five sets of facts which he claims supports the
theory that condensation nuclei are produced by atmospheric reactions of
volatile organics. One bit of evidence is the Tyndall experiment involv-
ing the passage of light through amyl nitrate or amyl iodide causing the
formation of a blue cloud. A second set of facts was derived from data
repeating the Tyndall experiment with terpenes which gave no cloud forma-
tion unless a "light absorbing catalyst" like NO. or I- is introduced.
The third experimental observation cited involved a nucleus counter in-
stead of the observation of visible smoke to indicate the formation of
condensed material. A 40-liter plastic bag with 1 ppm N02 and a few ppm
of terpene vapor took 10-15 minutes for the condensation nuclei to go
through peak value. The fourth piece of evidence offered was the obser-
vation that condensation nuclei buildups were functions of N02 concentra-
tion when a-pinene, NO- mixtures were irradiated with a 35-amp carbon
arc lamp. Finally, Went observes that the hot springs at Yellowstone
show a low condensation nucleus count on cold winter days; however, when
the sun is shining, he observes that greater amounts of NO- and a-pinene
12
-------
vapors are released, and the condensation nuclei count increases. The
ultimate fate of the condensation nuclei involves agglomeration at or
near the inversion layers in the atmosphere and then removal by
precipitation.
12
Cavanagh, Schadt, and Robinson report atmospheric measurements of
hydrocarbon composition at Point Barrow, Alaska, where they believed that
they were sampling essentially unpolluted air indicated by the low level
of condensation nuclei. Probably the most striking observation of their
series was the anomalously high level (about 100 ppb) of n-butanol observed
in these air samples. It is notable that the first report of these mea-
surements in Ref. 5 showed values of n-butanol about 9 times lower than
the values in this paper. No explanation was given for this disparity.
One might conclude that the published version of their project report
contained more careful calibration and data reduction procedures. They
also noted that acetone levels were somewhat higher than they would expect.
All of the hydrocarbon concentrations seemed to go down with increase in
wind speed as if they were locally produced near the ground. The authors
hypothesize that the compounds that they observed are the oxidation pro-
ducts of fermentation of decomposing tundra. Included in these products
could be n-butanol, acetone, and acetaldehyde. They point out that mea-
surements show that the local surface temperature in the tundra gets near
100°F while the air temperature only a few feet above the surface is only
at 60°F. Cross-checks on the specificity of their analysis techniques
for n-butanol were made by using three different gas chromatographic
adsorption media. The average concentration levels they observed were
methane: 1.6 ppm, butane: 0.06 ppb, acetone: 1.0 ppb, and n-butanol:
190 ppb. Table 3.1 summarizes a 24-hour analysis sequence made on
September 2 and 3, 1967. Notable is the low level of condensation nuclei
in the last column. It is difficult to discern any specific diurnal pat-
tern of the concentrations of the oxidized hydrocarbons.
13
-------
TABLE 3.1
CARBON MONOXIDE AND ORGANICS IN THE ATMOSPHERE, PT. BARROW
ALASKA; 24-HR ANALYSIS, SEFTIMEER 2-3, 196712
Date
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/2/67
9/3/67
9/3/67
9/3/67
9/3/67
9/3/67
9/3/67
9/3/67
9/3/67
9/3/67
9/3/67
Time
1030
1140
1230
1340
1440
1500
1550
1630
1730
1820
1930
2050
2145
2230
2330
0030
0130
0230
0330
0430
0530
0630
0730
0830
0930
Ethane,
Ethylene,
ppb
0.04
0.04
0.03
0.03
0.03
0.06
0.05
0.08
0.06
0.03
0.06
0.03
0.06
0.05
0.05
0.02
0.05
0.04
0.05
0.05
0.04
0.04
0.06
0.05
Butane,
ppb
0.19
0.05
0.04
T
0.03
0.08
0.06
0.11
0.04
0.04
0.08
C.05
0.06
0.03
0.05
0.03
0.05
0.03
0.05
0.03
0.04
0.1
0.1
0.1
Pentane,
ppb
0.1
**
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nu
0.09
0.1
0.2
0.1
0.2
0.1
nd
0.2
0.3
0.08
nd
nd
Unknown
(1),
ppb
2.3
3.0
3.3
6.9
9.4
3.4
1.8
1.6
1.6
1.2
1.1
0.4
0.4
0.2
0.3
0.3
0.3
0.3
0.3
1.1
0.5
0.9
1.4
1.4
1.7
Acetaldehyde,
Ppb
0.2
0.3
0.3
0.2
0.3
0.1
'
t
t
'
t
>
t
t
t
t
t
t
0.3
t
t
t
t
t
Acetone,
ppb
1.6
nd
1.5
2.7
2.9
1.9
0.9
0.9
1.3
1.1
0.3
nd
nd
0.8
0.9
1.2
0.9
1.0
0.7
0.7
1.1
0.9
1.0
1.1
1.3
Unknown
(2),
ppb
0.3
0.2
0.2
0.3
0.5
0.2
r
J.
0.2
t
-t
t
t
t
t
t
t
0.4
t
t
t
t
t
f
t
Methanol,
Ethanol ,
ppb
0.5
0.5
0.9
t
f
0.7
t
1.2
t
0.9
0.9
-b
0.7
0.9
0.9
0.9
t
0.4
t
0.7
0.7
0.7
0.7
0.9
Unknown
Benzene, (3)_
PP" ppb
v 0.4
t 0.4
t t
t 0.4
0.4
+ 0.3
T +
t t
t 0.4
t 0.5
t 0.4
t 0.4
t 0.2
t t
t 0.3
0.1 0.4
t 0.3
0.4 0.2
0.1 0.3
t 0.3
0.1 0.4
0.1 0.3
t 0.3
t 0.4
^ 0.4
Unknown
(4),
ppb
0.2
0.5
0.1
0.3
0.2
0.3
0.2
0.2
0.3
0.2
0 2
0.4
0.3
0.3
-
t
*
-
-
<
f
-
~
'i-Butanol ,
ppb
96
96
73
91
91
81
97
111
126
121
83
99
H3
76
74
68
57
51
73
86
107
S3
93
92
90
Methane,
ppb
1.4
1.52
nd
1.52
1.41
1.4
1.46
nd
1.39
nd
1.43
1.35
1.15
nd
nd
nd
nd
nd
1.48
1.50
1.50
nd
1.55
1.55
1.65
Carbon Condensation
Monoxide, Nuclei,
ppb n/cnt^
122 0
89
64
146 0
125
nd
134 0
105
127
102 100
119
nd Ci
10?
119 0
100
107
80
119 ?00
123 IOC
90
97
110
105
105 0
9? 0
Composite peak.
nd - no data, instrument difficulties.
'Not detected.
-------
Rasmussen in his paper on isoprene emissions from forests, specu-
lates briefly on the fate of isoprene and a-pinene in the atmosphere. He
believes that they are consumed in a photochemical mechanism involving
smog reactions between these compounds, oxides of nitrogen, and sunlight
forming ozone peroxyacylnitrate-like compounds as well as aerosol material.
He further suggests that there may be a biological pathway for removal of
these materials by their utilization by wild populations of fungi that
take up compounds as a carbon source for their growth. It would appear
from the data that once emitted, however, these compounds are very rapidly
consumed in gas phase reaction processes. 1,3-butadiene, structurally
related to isoprene, is a prime substrate for the production of oxidized
compounds like acrolein and formaldehyde, as well as peroxyacetylnitrate
(PAN). The identification of these products has been reported by Stephens,
13 14
Darley, Taylor, and Scott, and in a subsequent paper Stephens and Scott
compared the reactivity of various hydrocarbons in polluted atmospheres.
One of the compounds tested was pinene. Table 3.2 shows the hydrocarbon
disappearance rates, the PAN formation, and the aldehyde formation observed
in these experiments. It is noted that pinene is a fairly reactive com-
pound, however, it is not nearly as reactive as the internally double-
bonded olefins such as the butenes. In his comparison of product yields
and effects caused by various organics photooxidized in the presence of
oxides of nitrogen, Altshuller rates diolefins and dialkyl and trialkyl-
benzenes high on the reactivity scale. On a 0-10 scale for ozone produc-
tion, these compounds range from 6-10. Aerosol production ranged from 4-10
and curiously, plant damage ranged from 5-10 on this scale. These fami-
lies have compounds which average 6 in their total response on the reacti-
vity scale. Of the compounds tested by Altshuller these come closest
(in a chemical reactivity sense) to the terpene compounds emitted as
hydrocarbons from natural sources.
Rasmussen and Holdren used a portable "cryocondenser" to obtain
air samples in remote areas. They claimed that this device essentially
completely condensed both the air and its contaminants. They analyzed
15
-------
TABLE 3.2
REACTIVITY AND PRODUCTS OF PHOTOCHEMICAL OXIDATION OF 5 ppm EACH HC + N02 (STEPHENS AND SCOTT14)
FAN Formation
Aldehyde Formation
KC Disappearance HC Half
Compound ^^ (ppm.hr-l) Time (hr)
Ethylene
p-xylene
o-xylene
Durene
Mesitylene
m-y.ylene
Propylene
Iso butene
cis-2-butene
cis-3-hexene
Tetramethyl-ethylene-
Pinene
p-Mentha-1 , 5-Diene
0.
1.
1:
1.
1.
2.
3.
5.
22
18
?ci
5.
30
83
1
2
1
7
9
8
2
8
3
2 1/3
2
2
1 I/O
1
3/4
2/3
1/10
1/6
i/10
2/3
1/4
ppm-
0
0.
0.
0.
0 .
0.
0.
0.
1.
G.
-
-
-
hr-1
11
14
28
38
27
30
30
10
88
--
--
Maximum
Concentration (ppm)
0
0
0
0
o
0
>0
0
0
0
0
c
.38
.42
.70
.78
.54
.55
.31
.78
.75
.25
.23
Max imum
Concentration (ppm)
2
1
1
2
3
1
3
3
5
5
-
1
y
.2
.3
.1
. 3
= 0
.3
.3
.0
.0
.0
.3
.0
Peroxyacetylnitrate.
-------
their samples with a gas chromatograph using a flame ionization detector.
This chromatograph had the capability of temperature programming. It is
notable that they did not calibrate the device for n-butanol. It would
have been interesting, for example, to compare their results for n-butanol
12
with the results of Cavanagh, Schadt, and Robinson. Rasmussen and Holdren
obtained ground samples and aircraft samples and got nearly the same re-
sults over a forested mountain area. The chromatograms for these tests
exhibited relatively large peaks for acetone, benzene, and a few unidenti-
fied hydrocarbons. They showed little isoprene or a-pinene. In another
test, onshore air moving inland from the ocean on the Olympic Peninsula
was sampled. Benzene and toluene showed up in the samples suggesting
the presence of gasoline vapor contamination. Samples near the surf area
at Point Reyes National Seashore (California) showed a large, unidentified
peak in the area of C,. hydrocarbons and another large peak that might be
identified as methylpentene or cis-2-hexene. The samples showed only small
peaks at the pinene location on the record. Other samples were obtained
in Hells Canyon (Snake River) in order to determine what the air ir.ight
contain in an area that had very little vegetative cover. Large peaks
here were noted in the compounds acetone, hexene, benzene, and d-limonene.
Also, a large cluster of peaks were observed near octane. These results
suggest a mixture of oxidation products, some substances from raw gasoline
vapor, and some naturally emitted hydrocarbons. They also took samples
in the evening at a forested campground on the Olympic Peninsula. The
campground results showed higher composition of terpenes because of the
proximity to a forest and the possibility of campfire wood smoke contami-
nating the air parcel. It was recommended that many of the unidentified
compounds be sorted out by a gas chromatographic analysis employing a
mass spectrograph on the output.
17
-------
4 CONCLUDING REMARKS AND PRELIMINARY RECOMMENDATIONS
4.1 SUMMARY OF OBSERVATIONS AND EVALUATION
Estimates indicate that reactive hydrocarbon contributions from
natural sources far exceed those from anthropogenic sources. In order
to enlarge the body of knowledge of emission rates from natural hydro-
carbon sources, measurements should go beyond the types of vegetative
cover presently identified. The additional information should include
species identification, their sources and their reaction mechanisms
leading to haze formation. Table 4.1 summarizes the literature reviewed
above. Under the hydrocarbon section of the Global Budget Panel's report
from the Chemist-Meteorologist Workshop (sponsored by AEC and EPA), it
was recommended that the following three topics be studied:
1. The sources of HC and their strengths (including man-
controlled sources).
2. The identity of intermediate oxidation products including
gas phase oxygenates as well as aerosolized material.
3. The mechanisms by which organic aerosols are formed.
Regarding the knowledge of emission rates, it would be desirable to im-
plement a measurement program with the objective of improving the -in situ
measurements. The role of transport is totally unknown in experimental
results involving samples taken within plastic covered frames and above
foliage canopies. Samples must be taken at various heights under known
meteorological mixing conditions. The design of such a program would
necessitate taking wind, temperature, and humidity measurements at
various vertical height stations. Oxygenates and aerosols should be
measured as well as the terpene species. But these recommendations will
be fully detailed in the next section. Let us turn first to an evalua-
tion of what has been presented in the literature.
Many of the deductive calculations of emission rates in the liter-
ature cited above are suspect because of the almost total lack of
18
-------
TABLE 4.1
SUMMARY OF LITERATURE REVIEWED IN ORDER OF REFERENCE NUMBER
Reference
Went1'2
Rasmussen
and Went 3
Ripperton ,
Whice and
Jeffries*
Robinson
and Robbins
Rasmussen
Sanadze and
Dalidze8
Rasmussen
Went11
Cavanagh ,
Schadt and
Robinsonl2
Rasmussen
and Holdren
Groblicki
and Nebel23
24
Lillian
Ripperton
and Lillian25
26
Ripperton,
Jefferies and
White
Year
1960
1965
1967
1968
1970
1962
1972
1966
1969
1972
1971
1972
1971
1972
What Vege-
tation Type
Coniferous
forest ,
Sagebrush
Hardwood
forest
Hardwood
forest ,
Juniper, Aspen,
Pine forest
All types
Trees
amorpha fruti-
cosa , buxus ,
quercus iberica
Trees
Trees
Tundra
Forest ,
seashore,
barren
Not applicable
Not applicable
Not applicable
Not applicable
What Compounds?
Isoprene derivations
Isoprene, a-Pinene,
B-Plnene, A-Carene
Mycene , a-Limonene
Paracymene
a-pinene, ozone
B-pinene
Reactive
hydrocarbons
Isoprene
Isoprene
Isoprene
a-pinene
Altken nucleii
Many hydrocarbons
and carbon
monoxide
Many hydrocarbons
a-pinene, aerosol
a-pinene, oxidant
03, N02, NO
condensation nucleii
a-pinene, oxidant
0., , N09 , NO, H~0
condensation nucleii
a-pinene ,
1 , 5-Hexadiene
Cyclohexene,
2-Hexene, HjO
0.,, aerosol
Were Em
measured?
No
Yes
No
No
Yes
Yes
Yes
No
No
No
No
No
No
No
^ssions
estimated?
Yes
Yes
' Yes
Yes
No
No
Yes
No
No
No
No
No
No
No
Were Ambient
Concentrations
measured?
No
Yes
Yes
No
No
No
No
No
Yes
Yes
No
No
No
No
Were Reaction
Kinetics
measured? estimated?
No No
No No
Yes No
No No
1
No 1 No
No No
No No
No Yes
No ' No
No No
1
!
Yes ; No
Yes , No
Yes No
Yes ' No
i
19
-------
consideration of competing atmospheric processes like diffusion or re-
moval. Much of the early work is based almost totally on speculation
regarding the fate of the organic plant materials during conditions of
growth, metabolism, and dormancy. The lengthy descriptive passages lack
quantitative substantiation. Some of the attempts at order-of-magnitude
calculations are plagued with numerical errors. If these difficulties
are rectified as recommended, it is likely that the high degree of scatter
(by factors of over 30) could be resolved by some careful measurements
that are interpreted using modern reactive-diffusion computational methods.
(The specific recommendations are enumerated below.)
Turning to the present state of knowledge of concentrations and
atmospheric processes of naturally emitted reactive hydrocarbons, we note
again that the observations are spotty and, with few exceptions, in a
relatively primitive state. Conjecture regarding the ozone-terpene mecha-
nism leads to downright confusing statements such as
Since 03 can be synthesized in the photooxidation of pinenes
[by 03] the net destruction [of 63] could be reduced further.
Thus the 03-pinene and related reactions represent the most
important 'sink' for a-pinene and B-pinene, but are probably
of minor importance as an 63 sink.
4
This comes from one of the more definitive papers and is likely to be
correct in its conclusions. Its reasoning could have been clarified con-
siderably by performing some kinetics calculations which are now fairly
routine, but were not available at the time of the work reported (1967).
Much of the gas phase measurement could be made more specific with regard
to compound identification by the use of such computations.
Taken as a whole, the body of information presently available on
the emission transformation and ultimate fate of naturally emitted hydro-
carbon compounds presents the following picture: vegetative cover seems
to be the chief source of terpenoid and hemiterpene emissions. If we
2
accept Went's estimate of 5 tons/yr/km for emissions and use a rate
-2 -1 -1 *
constant of 10 ppm -min for the ozone attack of terpene we can
*
For estimating purposes this value is taken to be the average between
the values reported for ozone on 1,3-butadiene by Hanst, et al.,18 and
that reported by Vrbaski and Cretanovic.19
20
-------
compute the rate of terpene removal versus the rate of terpene emission
over a vegetated area of the earth's surface. We will use for reactive
HC concentration a value of ^0.01 ppm (based on observed values from the
literature cited in previous sections). Values of ozone, nitric oxide,
and nitrogen dioxide concentrations are determined from averages of data
20
reported by Ripperton, Worth and Kornreich. They are: C^ = 0.03 ppm,
C - 0.002 ppm and CL =0.06 ppm and are found by roughly averaging
the measurements on the Piedmont. (Incidentally, these concentrations
22
are consistent with a photostationary equilibrium with a nitrogen
dioxide photodissociation rate of 0.25 min and an 0--NO rate constant
-1 -1
of 25 ppm «min both of which are reasonably representative of observed
values.) Multiplying the rate constant times the concentrations we obtain
a terpene reaction rate of 3 x 10 ppm'min . If we assume a mixing
21
height of ^1 km (which is representative for the United States ) the
9 f\ 1 &
5 tons/yr/km would cause a rate of increase of 2 x 10 ppm'min
The fact that these numbers are of comparable magnitude suggests that
ozone reactions consume the terpenes in the same region that they are
emitted.
It remains to be shown that the emissions can be mixed into the
atmosphere in a time equal to or shorter than the time it takes them to
react with ozone. The characteristic reaction time is taken to be the
terpene concentration divided by the reaction rate. We obtain c /
/I r *\ rlv^ /
dt| = 0.01/(3 x 10 ) or 3.3 x 10 /minutes for the reaction time.
The diffusion time to the 1-km mixing height can be estimated using a
2
random walk assumption that time = z /2D where z is vertical mixing
distance and D is diffusion coefficient. Consistent values for the
-5 2
atmosphere are z = 1 km and D = 10 km /sec. This gives a diffusion
3 3
time of 0.83 x 10 minutes which is a little less than the 3.3 x 10
*
The conversion from mass units to mole units assumes a hydrocarbon
molecular weight which is the average of isoprene's and pinene's mole-
cular weight.
21
-------
minute reaction time. Evidently atmospheric mixing is marginally suffi-
cient to allow reaction to take place with the atmospheric ozone.
Having shown that the emission rate is about offset by the reaction
rate and that mixing occurs fast enough to supply the reactant, we note
the apparent internal consistency in the following observations:
1. Naturally emitted reactive hydrocarbons occur in larger
quantity than do those from anthropogenic sources. ' ' '
2. Terpenes are at much higher concentrations in the immediate
vicinity of vegetative cover. ' ' ' '
3. Blue haze formation is likely to follow photooxidation
immediately (or even precede most of the reaction) based
, , , . 11,22,23,24,25,26
on laboratory observations.
4. The mechanism of photooxidation parallels closely that
* u «. u i ^ «. u 23,24,25,26
of photochemical smog in urban atmospheres.
5. Terpene atmospheric reactions probably do not perturb
4*
the background ozone significantly.
6. Photooxidation is likely to be the main removal mechanism
for naturally emitted reactive hydrocarbon.
7. In areas remote from vegetation, the terpene compounds
have mostly reacted to form hydrocarbons in various
levels of oxygenation; especially alcohols, ketones,
, . , , , 12,16
and aldehydes.
4.2 PRELIMINARY RECOMMENDATIONS
Although these tentative conclusions seem internally consistent,
they cannot tell the whole story; therefore, several elements of further
investigation are needed to clarify the following questions:
What is the source distribution of reactive hydrocarbons
in space and time?
*
This point needs further investigation.
22
-------
What is the composition profile of naturally emitted
reactive hydrocarbons?.
What relationship exists between the natural hydrocarbon
cycle and the background ozone concentrations?
* What are the natural pathways for transformation of
naturally emitted reactive hydrocarbons?
What is the ultimate fate of these compounds?
How do these compounds and their derivatives impact on
man and the remainder of the terrestrial ecosystem?
Some specific areas of research should be undertaken to answer these
questions. They are:
1. Expand the scope of the cryocondenser sampling and
utilize spectroscopic analysis with the gas chromatograph
to identify compounds more specifically than before.
2. Source characterization should be improved by taking more
In situ measurements over different types of cover.
3. Atmospheric in situ measurements should incorporate ver-
tical profiles of both chemical species concentrations
and meteorological variables over natural source areas.
4. Prior to any extension of the experimental program, reac-
tive diffusion calculations should be carried out using
existing models to determine:
a. The fate of natural hydrocarbons
b. The role of natural hydrocarbons in the background
ozone balance.
*
Ideally, measurements should include ozone and oxides of nitroge;n as
well as the various hydrocarbon compounds.
23
-------
c. The relative likelihood of natural versus anthro-
pogenic hydrocarbons causing the occasional high
ozone levels observed in remote areas.
d. The best design of an -in situ experimental field
program with regard to answering the six questions
listed above.
24
-------
REFERENCES
1. Went, F. W. , "Organic Matter in the Atmosphere and its Possible
Relation to Petroleum Formation," Proc. National Academy Sciences,
Vol. 46, pp 212-221.
2. Went, F. W., "Blue Hazes in the Atmosphere," Nature. Vol. 187
No. 4738, pp. 641-643 (August 20, 1960).
3. Rasmussen, Reinhold A., and Went, F. W., "Volatile Organic Material
of Plant Origin in the Atmosphere," Proc. National Academy Sciences.
Vol. 53, pp. 215-220 (1965).
4. Ripperton, L. A., White, 0., Jeffries, Harvey E., "Gas-Phase Ozone-
Pinene Reactions," American Chemical Society 154th Meeting, Chicago,
Illinois, Sept. 10-15, 1967, Division of Water, Air and Waste
Chemistry, p. 23.
5. Robinson, E., and Robbins, R. C., "Sources, Abundance, and Fate of
Gaseous Atmospheric Pollutants," Stanford Research Institute Report
PR-6755, February 1968.
6. Rasmussen, Reinhold, A., "Isoprene: Identified as a Forest-Type
Emission to the Atmosphere," Environmental Science and Technology.
Vol. 4, No. 8, pp. 667-671 (8 August 1970).
7. Gil-Av, E., and Shabtai, J. "Precursors of Carcinogenic Hydrocarbons
in Tobacco Smoke," Nature. Vol. 197, No. 4892, pp. 1065, 1066
(March 16, 1963).
8. Sanadze, G. A., and Dolidze, G. M. , "C,.HQ (isoprene) type Hydro-
carbons in Volatile Emissions from the Leaves of Plants," Soobishch.
Akad. Nauk Gruz SSr. Vol. 27, p. 747 (1961); Chem. Abstr.. Vol. 57,
p. 1222 (1962).
9. Hancock, J. L., Applegate, H. G., and Dodd, J. D., "Polynuclear
Aromatic Hydrocarbons on Leaves," Atmospheric Environment, Vol. 4,
No. 4, pp. 363-370 (July 1970).
10. Rasmussen, R. A., "What Do the Hydrocarbons from Trees Contribute
to Air Pollution," Journal of the Air Pollution Control Association.
Vol. 22, No. 7, pp. 537-543 (July 1972).
25
-------
REFERENCES (Cont.)
11. Went, F. W., "On the Nature of Aitken Condensation Nuclei!," Tellus.
Vol. XVIII, No. 2, pp. 549-556 (1966).
12. Cavanagh, L. A., Schadt, C. F., and Robinson, E., "Atmospheric
Hydrocarbon and Carbon Monoxide Measurements at Point Barrow,
Alaska," Environmental Science. Vol. 3, No. 3, pp. 251-257 (March
1969).
13. Stephens, E. R., Darley, E. F. Taylor, 0. C., and Scott, W. E. ,
"Photochemical Reaction Products in Air Pollution," Proceedings
of the American Petroleum Institute, Vol. 40 [III], pp. 325-328
(1960).
14. Stephens, E. R., and Scott, W. E. , "Relative Reactivity of Various
Hydrocarbons in Polluted Atmospheres," Proceedings of the American
Petroleum Institute. Vol. 42 [III], pp. 665-670 (1962).
15. Altshuller, A. P. "An Evaluation of Techniques for the Determination
of the Photochemical Reactivity of Organic Emissions, Journal of
the Air Pollution Control Assoc.. Vol. 16, No. 5, pp. 257-260
(May 1966).
16. Rasmussen, R. A., and Holdren, M. W., "Analyses of C5 to C^Q Hydro-
carbons in Rural Atmospheres, Air Pollution Control Association
Paper #72-19 Presented at 65th Annual Meeting, June 18-June 22,
1972.
17. Chemist-Meteorologist Workshop-1973, Ft. Lauderdale, Florida,
January 15-19, 1973, p. 25.
18. Hanst, P. L., Stephens, E. R. , Scott, W. E., and Doerr, R. C.
"Atmospheric Ozone-Olefin Reactions," paper at the 136th Meeting
of the American Chemical Society, Atlantic City, N.J. (1959).
19. Vrbaski, T., and Cvetanovic, R. J., Canadian Journal of Chemistry
18:1053 (1960).
20. Ripperton, L. A. , Worth, J. J. B., and Kornreich, L., "Nitrogen
Dioxide and Nitric Oxide in Non-Urban Air," Journal of the Air
Pollution Control Association. Vol. 20, No. 9, pp. 589-592
(September 1970).
21. Holzworth, G., "Mixing Heights, Wind Speeds, and Potential for
Urban Air Pollution Throughout the Contiguous United States," U.S.
Environmental Protection Agency AP-101, pp. 26-35 (January 1972).
26
-------
REFERENCES (Concl.)
22. P. A. Leighton, Photochemical Aspect of Air Pollution. Academic
Press, New York, N.Y. (1961).
23. Groblicki, P. J., and Nebel, G. J., "The Photochemical Formation
of Aerosols in Urban Atmospheres," in Chemical Reactions in Urban
Atmospheres. C. S. Tuesday, ed., American Elsevier Publishing
Co., Inc. (New York, 1971) pp. 241-267.
24. Lillian, D., "Formation and Destruction of Ozone in a Simulated
Natural System (Nitrogen Dioxide + a-pinene + hv)" in Photochemical
Smog and Ozone Reactions. R. F. Gould, ed. Advances in Chemistry
Series 113, American Chemical Society (Washington, 1972) pp. 211-218.
25. Ripperton, L. A. and Lillian, D., "The Effect of Water Vapor on
Ozone Synthesis in the Photooxidation of Alpha-pinene," Journal of
the Air Pollution Control Association. Vol. 21, No. 10, pp. 629-
635 (October 1971).
26. Ripperton, L. A., Jeffries, H. E., and White, 0., "Formation of
Aerosols by Reaction of Ozone with Selected Hydrocarbons," Photo-
chemical Smog and Ozone Reactions, R. F. Gould, ed. Advances in
Chemistry Series 113, American Chemical Society (Washington, 1972),
pp. 219-231.
27
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28
------- |